Intermediate product in the manufacture of cellulose acetate



May 5,1925. y .1,536,311 v lP. C. SEEL INTERMEDIATE P RODUCT IN "THE MANUFATURE 0F' CELLULosE ACETATE original Filed Aug. 1s, 1925 14 A y 1Q I 'iii l v 17 condens/ng 2 @WMW Patented Mays, 1925. y

UNITED 'STATES'- PATENT. oFFic-E.

PAUL SEEIQ OF ROCHESTER, NEW YORK, .AASSIGNOR TO EASTMAN KODAK COMPANY,

a 'OF ROCHESTER, NEW YOBK,A CORPORATION NEW YORK;

vrirrnnivt mirare PRODUCT IN THE MAUFAGTURE'OF CLLULOSACETATEJ continuation of appiicaiioii seiiai ira-658,109, med August is, 192e..v serial No. 703,797.

t" and Stateof New York, have invented certain new and useful Improvements in an p 4 IntermediateProduct in the Manufacture.

of Cellulose Acetate, of whichthe following i isa full, clear, 'and exact specification.

This invention relates to an intermediate 4product in the manufacture of cellulose acetate. One object 'of the invention is to. provide an intermediate product-in a form `having large surfacerelative to is mass, to vfacilitate its treatmentfby liquids in the further steps of manufacture. `Another object is to provide suchen intermediate prod,- uct in a powdery form, in whiclnthe grains remain substantially separate without coalescing when stored .at room temperature and pressure, so that when treated byv liquids, the action will be substantially uniform on 4all particles, thereby avoiding lack of `homogeneity in thefiinal. cellulose acetate product. Other objects will hereinafter appea-r. j i AIn the drawing, y

`Fig. 1 isa diagrammatic side elevation,

vpartly in verticalsection, illustrating one form of yapparati'is in which the .process of preparing my intermediate product may be carried out, the relative sizes of the parts being exaggerated for the-sake of clearness,

lFig. 2 is a horizontal sectional .view of the mixing unittaken on `the 'lin'e'Qf-Z of Fig. 1. This application is a continuation of my prior application No. 658,109, led Aug. i18,

1923 Patent N o. 1,494,816, 'May 20, 1924: forA process ofyinanufacturing cellulose" acetate. As a result of that process there was produced a. powdery niassthe grams o r partivcles lofwhicli comprised cellulose acetate mixed -withacetic values.

The latter were not, however, present in such quantities, at

least on the surfaces ofthe particles, as to' cause the grains to coalesce. In the other words, the grains remained substantially separate when stored at ,room temperature and pressure. In this way this intermediate product retained its'very large surface relative to its massfacilitating its treat- 7 ment in further4 steps of the ,process with n This application filed April 2, 1924.

solvent liquids, washing liquids, or the like.

This intermediate product may be made by .one manufacturerandshipped to another,

hereinabove cited prior 1 application, and will 'now`be described by way of illustra-- tion..

Cellulose acetate is produced by the action of suitable acetylating agents on cellulose inthe presence of-catalysts. The re- I-various liquids, such as hydrolyzing baths, A

action mixture may,'for example, initially comprise cellulose, acetic anhydride acetic acid,`and' sulfuric acid, and the products of" the reaction as the latter proceeds. An eX- ainple of this general type isgiven in United States Reissue Patent No. 12,637,.Miles, Apr.

"23,` ,190?. The acetylating reaction is at firstvcarried on until a' chloroform-soluble cellulose acetate isA produced. Then a hydrolyzing mixture containing a relatively small amount of water is introduced until the reaction yconverts -the cellulose acetate into the acetone-soluble form. Before the hydrolying mixture acts, .the excess orV unused acetic anhydride 1s converted into aceticA acid 'by the addition of the proper amount of water. ASi'itiicient watei`- can be introduced in the hydrolyziiigmixture to kill the acetic anhydride and cooperate in the conversionv of the cellulose acetate.

If the reaction is terminated when the cellulose acetate is in. the chloroform-soluble 'stage,'a considerable amount' of acetic values remain, such as' acetic anhydride and acetic acid (andinsome cases acetyl chloride). If the reaction be carried to the point where acetone-soluble cellulose acetate is produced,

the acetic values will be in the form of acetic p acid'. Because of the relatively high. value ofvtlies'e' acetic values, they have a very iinportant bearing upon the cost of the cellulose acetate which is produced. Their recovery in good condition, when effectedinexpensive-` ly, lowers the total cost of the manufacturing operations and thereby cheapens the cost of thepioducqand I have beenl able to obtain vsuchresult while securing said intermediate product-in the form of a'powdercontaining iccA cellulose acetate having many valuable properties. V

, The reaction mixture has heretofore been washed with a considerable excess of water to freeA it from the acetic values. The recovery of these values from the comparatively dilute solutions which are produced can be carried out only 'at considerable expense. Tater evaporating steps and chemical reaction steps have proven to be complicated and undesirably expensive.

I have found that the desired intermediate product can be made and the recovery of the acetic values can be 4simply and inexpensively carried out bysep'arating at least the major portions of the acetic values from the reaction mixture by means of a gaseous vehicle, such as air. Preferably I pass the vehicle through the reaction mixture to take up vapors of the acetic values and then recover the values from the laden vehicle by condensation, absorption, or the like.r I have found it preferable to pass the gas through the reaction mixture in a subdivided form, such as by forcing air bubbles through it, so that a large amount of surface is presented through which vapors of the acetic values may enter the gas. The reaction mixture is, broadly speaking, liquid, by which I mean that it is flowable to a certain extent, even when it is sometimes thickened to a pasty condition.

I have likewise found that the manufacture of the novel intermediate product and the recovery of the acetic values are greatly facilitated by -repe-atedly circulating the gaseous vehicle, suchl as air, through the reaction mixture and the Zone or sl ation where the acetic values are removed from it. This recirculation enables the use. of a stronger concentration of the vapors of acetic values in the air current, vfacilitating condensation, and prevents an unremoved fraction of these values being wasted in the manner that would take place if the air wer-e discharged into the atmosphere to carry away the unextracted vapors.A

` I have also discovered that when the gaseous vehicle is agitated through the reaction mixture for a suliicient time the latter changes from a liquid or viscous form to a mass of separate particles ofa somewhat powdery nature. The aggregate surface of these particles is much greater than the surface of the4 original reaction mixture. I have found that advantage canbe taken of this large surface in the treatment of additional amounts of reaction mixture. lVhen these amounts are stirred into the powdery mass and a gaseous vehicle is passed thro-ugh, the additional amounts of reaction mixture are quickly converted to a subdivided or powdery condition, because of the increased rapid evaporation taking place from the enlarged surface.

My process may be carried outin many types of apparatus, the one shown in ,the drawing being merely illustrative of a useful form. The main receptacle in nhich the gaseous vehicle and reaction mixture are brought into intimate contact is indicated at 1. This is preferably an airtight vessel, except for the piping hereinafter described. It may conveniently take the form of a well known mixer in which the bottoln is divided into two troughs 2, 3 above which are located mixing blades 4l rotated with shafts 5, driven by any suitable means (not shown). These blades may be of a form which merely turns the material about; the shafts, but I prefer to use blades which give a longitudinal movement to the mixture also. See, for example, U. S. Patent No. 534,968, Peiderer, Feb. 26, 1895. The receptacle may be temperature controlled' by steam jackets or coils or any other well known and customary way.

Entering into the reaction mixture 6 is a perforated transverse pipe `7. This connects with a vertical pipe 8 Which passes through an airtight connection in the top 9. Pipe 8 is in turn connected by pipe line 10 with an air compressor or blower 11. The latter draws its supply of air through pipe 12 from the removal or recovery unit 13, which is in turn connected by pipe 14 with the top 9 of receptacle 1. In the top 9 of the receptacle 1 there is also located -a normally closed or sealed loading fixture or pipe 15.

I find it useful to have a heating Aunit 16 -for slightly warming the gaseous vehicle before it enters the main mixing receptacle' 1. This is indicated diagrammatically in the drawing as a casing 17 4surrounding a section of pipe 10, through which Warm water or exhaust steam is passed through pipes 19 controlled by valves 20. The removal station 13` where vapors of acetic4 values (usually the vapors of acetic acid) are separated from the air, ma take the form of any well known absorpt1on or condensation tower. This is conventionally indicated m Fig. 1 as a cooling chamber 21- surrounding a coil 22, the cooling medium being passed in and out by'means of pipes 23 controlled by valves 24. The entrance of, additional air when required may be conveniently effected' by manipulating valve 25 in pipe 26.

In carryingr out my process in this apparatus a reaction mixture, such as any one of those shown at the different stages in the Miles patent cited above, is charged into receptacle 1 through pipe 15 until it rises above perforated pipe 7. The blades 4 are set in operation and the compressor or blower 11 started to force air through pipes l0, 8, and 7 into the reaction mixture 6.

The bubbles thus formed in the mixture are agitated or forced through the material, the blades 4 assisting in this action. During V without clogging the condenser.

this period the bubbles of the gaseous vehicle take upas much vapor of the acetic 4 values as they can hold at the prevailing.

oft through valves 27 in enlarged pipe 2 8. 'The amount. of vapor which isV condensed and i'eii'ioved at station-13 depends primarily upon the difterence i'n temperature betweenA it and receptacle 1. .The condensing temperature is kept as low as practical Without.

solidifyingv the acetic values which are condensed in it. .I lhave found 60 F. to be `uset'ul when there is a slight amount of water present. because it enables the acetic acid to be condensed in the liquid form This temperature. however. is, of course, subject t adiustment. as will 'be understood by those skilled inthe art. There will. of course, be some vapor of acetic values left inthe' air a tter it leaves the condenser and when it reenters the mixture 6, but they amount is sutliciently `below the saturation point to avoid interference' with the process. In tact. it assists the dividing of the mixture into small particles. and assists the rate of evaporation because it prevents too hard and impervious a skintorming on the pieces of the mixture. v

The cooled vehicle is drawn through pipe I2- bythe compressor or blower l1. yIt' av compressor is employed. it oftentimes warms the air up sufficiently to permit it to func tion properly when it passes through pipe to the receptacle 1. I have found this to bertrue in one forni ot apparatuswhere the compressor is operating at Jfrom 3 to 5 pounds'pressure. llVhen, however, the coinpresser does not adequately warm the verib hiele, or when a blower is employed, it is preferable to reheat the air to the required temperature (say or 900 F.) by means of heating unit 16. i

As the removal of the acetic valuesfrom 4the reaction mixture G progresses, the latter I add Jfurther amounts of reaction mixture v through pipe l5 and continue the circulation ot the air through the mass of reaction particles and the rest of the described apparatus. In this way the additional amounts of reaction mixture are distributed over the surfaces ofthe particles, which surfacesin the aggregate arerelatively large compared to that of the originalliquid.. In this way the circulating vehicle is repeatedly brought into contact with the additional reaction mixture and quickly removes vapors ot acetic values from .it- The powdery mass is increased by repeating the chargingr of additional reaction mixture and continuingT vthe blowing.. The powdery mass may thus be gradually built up until it approaches the top of receptacle l1. It. may then be removed through any suitable door, such as 29,'in receptacle 1.

The addition of the reaction mixture during` the building up of the powdery mass may be carried out intermittently or continuously, but in any 'event the rate of charging in' the mixture and the rate of passing the air'through. the mass are so cor related that ythe powdery condition will be kept up substantially enough to secure the advantages due toits increased evaporating surface.

Vhile the acetic acid vapors may be absorbed by bubbling' the vapor-laden air through a suitable liquid and then distilling the acid from such liquid, nevertheless I greatly prefer to use the condensation method described above, becauseit recovers..

thel acetic values in a. form sufficiently 'pure for re-use in further acetylation.

-The powdery mass` because ot ,its vry large surface relative to its weight., can be very i'apidlytreated by liquids in the further steps o't manufacture, such as by water for 4washing. or baths for further hydrolysis. or by solvents.

The evaporation of acetic alues i'rom the grains of powder may be carried out. un'til a veryvsmall portioniemains thereim-in fact, until the powder is so relatively tree fromsuch values thatI it can be utilized liiectly in' manufacturing' cellulose acetate plastics. As the'proportion ot acetic values in the grains grows smaller and smaller. the ditiiculty of drying' out or evaporatinp` awav the residue becomes increasingly more diticult. It is, therefore. often convenient to carry on the hereinabove described process until the acetic values constitute only a little less than 50% (say 80% for instance) ot the weight ot the powdery mass. This admits ot a quick and inexpensive recovery ot the biggest part. oi" the acetic values 'trom the -original cellulose acetate reaction mass. and

yet leaves an intermediate powdery product ot general utility in the best possible condition tor further treatment. v

bHaving thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1, As an intermediate product in they manufacture of cellulose acetate7 a powder,

the substantially separate grains of ivhieh compriseI cellulose acetate mixed with acetic ing substantially separate without ooalesoing at room temperature and pressure.

3. As an intermediate product 1n the manufacture of cellulose acetate, a cellulose 15 acetate reaction mass in powder form, acetic values being dried out of the grains thereof until the latter refrain from coaleseing at roomv temperature and pressure.

Signed et Rochester, New York, this 26thV 2U day of March, 1924.

' PAUL C. SEEL. 

